This invention relates to field coil assemblies for a dynamoelectric machine and more particularly to field coil assemblies particularly useful in a salient pole rotor of a dynamoelectric machine.
In a typical dynamoelectric machine, a plurality of field coil assemblies are mounted around the circumference of a substantially cylindrical rotor or a yoke of a magnetic material adapted to be rotatable about its central axis. Each field coil assembly comprises a magnetic pole of which a radially inner end is magnetically and mechanically coupled to the rotor by means of a dove tail projection that fits in a complementary slot formed in the axial direction in the cylindrical surface of the rotor. The radially outer end of the pole has formed thereon a mushroom-shaped pole shoe portion extending in both the axial and circumferential directions at the head portion of the pole. The field coil assembly also comprises a field winding wound around the pole for generating a magnetic flux extending radially through the hole. The field winding comprises turns of a rigid conductor bar, electrical insulations between the turns, and another annular insulating member having a U-shaped cross-section that is placed on the inner peripheral surface of the coil as well as the top and the bottom surfaces of the coil. This coil assembly is sandwiched between an upper and a lower insulating collar at the top and the bottom surfaces thereof and placed around the magnetic pole of the machine. Frequently, an adjusting rigid liner which is an annular member extending over the entire flange portion of the insulating member is inserted between the lower insulating collar and the peripheral surface of the rotor.
It is a usual practice that end portions of the cylindrical rotor or the yoke are partially removed at the region facing the inner face of the end turn of the coil or the region at the axial end portions of the pole. Therefore, the end turns of the coil are not directly mechanically supported by the rotor in the radially inner direction but are cantilevered owing to the rigidity of the coil and the electrical insulations, and this cantilevered coil end portion is spaced apart by a predetermined distance from the circumferential surface of the rotor.
Therefore, if the above distance was utilized as an electrically insulating distance or gap, then the electrically insulating materials are not necessary at least at this portion of the coil, and significant reductions in the amount of insulating material and cost can be expected.